This invention relates to apparatus for locking the door of a freight transporting compartment or the like, and particularly relates to door-locking apparatus which can be controlled by pneumatic pressure derived from the typical air brake system of the transporting vehicle.
In the effort to improve theft-resistant locks, door locking devices for freight transporting compartments have been developed which are controlled and operated by pneumatic pressure derived from either an auxiliary system or from a branch line communicating with the air brake system typically installed on railroad cars and truck trailers as described, for example, in U.S. Pat. Nos. 3,614,147; 3,624,761; and 3,843,174. The last-mentioned patent describes an anti-theft door-locking apparatus in which the locking pin is selectively movable between an active position in which the door is locked and an inactive position allowing the door to be opened; the apparatus also includes an operation-inhibiting means in the form of an abutment component or a detent and recess arrangement to hold the locking pin in its inactive position in order to prevent inadvertent or unauthorized return movement of the locking pin into the active position.